Graphite-based structures or devices, e.g. graphene quantum dots, graphene nanoribbons (GNRs), graphene nanonetworks, graphene plasmonics and graphene superlattices, exhibit many exceptional chemical, mechanical, electronic and optical properties, and are very desirable for use in electronic devices, composite materials, and energy generation and storage. Such graphite-based structures in general comprise a graphene layer, typically nanometers thick and having a characteristic dimension also in the nanometers range. For example, in order to obtain adequate band gaps for operation at room temperature, GNRs typically have a width within a few nanometers due to the inverse relationship between the band gap and the width of the GNRs. The specific geometrical requirements impose challenges on the development of fabrication methods that can produce graphite-based structures with controllable and reliable topography to achieve desired functionalities.
Another challenge in the development of fabrication methods is related to packing density. The ability to pack structures and devices onto a surface with high packing density is an important issue. Because packing density or workable surface area determines functionalities of devices such as efficiency of solar cells or detectors, extensive work has been dedicated to isolation of graphene layers and attempted to reduce or eliminate workable surface area loss. However, current techniques use horizontal isolation, resulting in workable surface area loss and thus a dissatisfactory yield.
Current methods for fabricating such graphite-based structures are complicated, expensive, inefficient and highly inconsistent, and are mainly limited to laboratories. These methods can be broadly classified as epitaxial growth, chemical vapor deposition (CVD) growth, colloidal suspension, unconventional methods and exfoliation (See, e.g., Jayasen and Subbiah, 2011, Nanoscale Research Letter, 6:95; Parrish, “Graphene Growth Techniques for Use in Nanoelectronics”).
Current fabrication methods generally involve patterning graphene, after graphene generation, into desired shapes and sizes. Patterning graphene, however, is very difficult because maintaining selectivity when etching carbon based materials is difficult in relation to other materials. It is in particular a notoriously difficult process in the nanoscale dimensions. As a result, current methods have several drawbacks. For example, the required etching for patterning graphene sheets into desired shapes often produce graphite-based structures with unpredictable geometries and erratic edge structures, yielding unsatisfactory functionalities of the graphite-based devices. Also, current methods generally use horizontal isolation, resulting in less usable surface area, lower packing density and accordingly lower efficiency of the graphite-based devices.
Given the above background, there is a need in the art for fabrication methods that can produce controllable, reliable and precise graphite-based structures without patterning the graphene layers, and in some cases, with multiple or enhanced functionalities.